U.S. patent number 6,357,671 [Application Number 09/489,835] was granted by the patent office on 2002-03-19 for ultrasonic nebulizer.
This patent grant is currently assigned to Siemens Elema AB. Invention is credited to Goran Cewers.
United States Patent |
6,357,671 |
Cewers |
March 19, 2002 |
Ultrasonic nebulizer
Abstract
An ultrasonic nebulizer includes a nebulization chamber for
holding a liquid to be nebulized, the liquid being limited by an
upper boundary within the chamber, and a nebulization source
acoustically couplable to the liquid within the chamber to provide
therein an ultrasonic output at an amplitude to cause nebulization.
The nebulization source is controllable to vary the amplitude of
the ultrasonic output to provide a measurement period during which
no nebulization occurs, and a sonar device measures, during the
measurement period, a time interval between emission of an acoustic
pulse toward the boundary and detection of a component of the
emitted acoustic pulse reflected from the boundary, and provides an
output signal dependent on the measured time interval for use in
determining location information of the boundary within the
chamber.
Inventors: |
Cewers; Goran (Lund,
SE) |
Assignee: |
Siemens Elema AB (Solna,
SE)
|
Family
ID: |
20414353 |
Appl.
No.: |
09/489,835 |
Filed: |
January 24, 2000 |
Foreign Application Priority Data
Current U.S.
Class: |
239/102.2;
239/102.1; 239/338; 239/67; 239/69; 239/71; 239/99 |
Current CPC
Class: |
B05B
12/081 (20130101); B05B 17/0607 (20130101); G01F
23/2962 (20130101); A61M 11/005 (20130101); A61M
2205/3375 (20130101); A61M 2205/3389 (20130101); A61M
2205/50 (20130101) |
Current International
Class: |
B05B
17/04 (20060101); B05B 17/06 (20060101); G01F
23/296 (20060101); B05B 001/08 (); A61M
011/06 () |
Field of
Search: |
;239/67,69,71,73,99,102.1,102.2,338 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
|
|
|
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0 151 753 |
|
Dec 1984 |
|
EP |
|
WO 93/09409 |
|
May 1993 |
|
EP |
|
0 845 663 |
|
Nov 1997 |
|
EP |
|
9-173978 |
|
Jul 1997 |
|
JP |
|
Primary Examiner: Evans; Robin O.
Attorney, Agent or Firm: Schiff Hardin & Waite
Claims
I claim as my invention:
1. A nebulizer comprising:
a nebulization chamber containing a liquid to be nebulized, said
liquid having an upper boundary within said nebulization
chamber;
an ultrasonic nebulization source acoustically coupled to said
liquid and operable to nebulize said liquid, said ultrasonic
nebulization source including a control unit which varies an
amplitude of ultrasound produced by said ultrasonic nebulization
source to provide at least a first measurement period and a second
measurement period during which no nebulization of said liquid
occurs, said first and second measurement periods being separated
in time from each other;
a sonar device disposed to measure, during each of said first and
second measurement periods, a time interval between emission of an
acoustic pulse toward said upper boundary and detection of a
component of said acoustic pulse reflected from said boundary, and
generating respective output signals dependent on said time
interval indicative of a location of said upper boundary of said
liquid within said nebulization chamber in said first and second
measurement periods; and
a difference former supplied with said output signals for comparing
said output signals to determine a change in the location of said
upper boundary of said liquid within said chamber, said difference
former emitting a difference former output signal dependent on said
difference, said difference former output signal being supplied to
said control unit to control at least one of an amplitude and a
duration of ultrasound from said ultrasonic nebulization source for
nebulizing said liquid within said nebulization chamber.
2. A nebulizer as claimed in claim 1 wherein said sonar device is
disposed to emit said acoustic pulse through said liquid to said
upper boundary.
3. A nebulizer as claimed in claim 2 wherein said ultrasonic
nebulization source comprises a piezoelectric transducer for
emitting said ultrasound with a variable amplitude, and wherein
said sonar device is also connected to said piezoelectric
transducer for emitting and detecting said acoustic pulse during
said measurement period.
4. A nebulizer as claimed in claim 1 wherein said ultrasonic
nebulization source is operated by said control unit to only emit,
during said measurement period, ultrasound having an amplitude
which causes substantially no disturbance to said upper boundary of
said liquid within said nebulization chamber.
5. A nebulizer as claimed in claim 1 wherein said ultrasonic
nebulization source is operated by said control unit during said
measurement period to emit ultrasound at a first amplitude for
producing a first location of said upper boundary and to emit
ultrasound at a second amplitude to produce a different location of
said upper boundary, and wherein said sonar device detects a first
output signal associated with said first amplitude and a second
output signal associated with said second amplitude, and wherein
said difference former uses one of said first and second output
signals as a reference signal and the other of said first and
second output signals as a measurement signal.
6. A nebulizer as claimed in claim 5 wherein said ultrasonic
nebulization source is operated by said control unit so that one of
said first and second amplitudes produces no disturbance of the
location of said upper boundary of said liquid within said
nebulization chamber.
7. A nebulizer as claimed in claim 4 wherein said difference former
includes a memory connected to said difference former for storing
the output signal from said first measurement period.
8. A nebulizer as claimed in claim 7 wherein said difference former
derives a difference between signals received from consecutive
measurement periods.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultrasonic nebulizer (atomizer)
and in particular to a nebulizer of the type having an output
controllable dependent on the level of liquid available for
nebulization.
2. Description of the Prior Art
Ultrasonic nebulizers are devices which utilize a source of
ultrasound, such as for example a piezoelectric crystal oscillator,
acoustically coupled to a liquid in a nebulizing chamber in order
to generate an aerosol of small liquid droplets in a space above
the liquid boundary. The generated aerosol may be used for any
desired purpose such as humidification or medication. Such
nebulizers are often used as a component in a breathing circuit of
a mechanical ventilator, where they are employed in the delivery of
controlled doses of anaesthetic or other additive into a breathing
gas for supply to a patient.
It is important, particularly in the medical field, to be able to
monitor the level of liquid in the nebulizing chamber. This may be
for example, in order to maintain a supply of liquid throughout
mechanical ventilation or to monitor the dosage of liquid delivered
into the breathing gas.
One known ultrasonic nebulizer which is provided with a liquid
level indicator is disclosed in U.S. Pat. No. 3,839,651. This
nebulizer uses a temperature sensitive resistance element which is
thermally coupled to the liquid within the nebulizing chamber. The
current in an electrical circuit containing this element is
dependent on the amount of liquid within the chamber and is used to
decrease power supplied to the oscillator and to provide a visible
indication when the liquid level falls to a predetermined minimum.
One problem with such a level indicator is that it is relatively
insensitive to small changes in liquid level which are likely to
occur between successive, or closely spaced, inspiration periods of
a patient breathing cycle.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an ultrasonic
nebulizer having a level indicator capable of sensing such small
changes.
The above object is achieved in accordance with the principles of
the present invention in a nebulizer having a nebulization chamber
containing a liquid to be nebulized the liquid having an upper
boundary within the chamber, and an ultrasonic nebulization source
which is acoustically coupled to the liquid to introduce ultrasound
into the liquid to nebulizer the liquid, and wherein the ultrasonic
nebulization source is operated to emit ultrasound with a variable
amplitude so as to provide a measurement period during which no
nebulization occurs, and wherein the nebulizer has a sonar device
which, during the measurement period, measures a time interval
between emission of an acoustic pulse toward said liquid boundary
and detection of a component of the emitted acoustic pulse
reflected from the boundary so as to produce an output signal
dependent on this measured time interval which is indicative of a
location of the upper boundary of the liquid within the
nebulization chamber.
By controlling the amplitude of the nebulization source to provide
periods where no nebulization occurs, possibly by providing periods
of zero amplitude output, a sonar device which employs echo ranging
techniques may be used to measure the location of the upper
boundary of the liquid within the nebulization chamber. This
provides a relatively sensitive arrangement for identifying changes
in the location of the liquid boundary from which, for example, the
amount of liquid within the nebulization chamber may be
calculated.
Preferably, a single piezoelectric crystal is employed as both the
nebulization source and as the sonar device. This allows existing
nebulizing chambers and sources to be used with only modifications
to the electronic circuitry used to control the crystal being
necessary. Moreover, by using only one crystal, a major component
cost saving is achieved compared with employing separate sonar and
nebulization sources.
A difference forming circuit is used to enable differences in the
location of the liquid boundary to be determined. The determined
difference, for example, may be used to monitor the amount of
liquid nebulizer between measurement periods or to monitor the
effect of different known crystal driving currents on the liquid
boundary during a single measurement period. Both of these
monitoring modes then may be employed to calibrate the nebulization
source and to control the amplitude or duration of the ultrasonic
output from the source to, for example, more reliably provide a
required amount of nebulization or to remove power from the source
if a minimum liquid level is reached.
Particularly useful is the latter mode of monitoring since a
calibration of the output of the nebulization source may be made
before generating any nebulized liquid.
DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic representation of an embodiment of a
nebulizer and illustrates one mode of operation according to the
present invention.
FIG. 2 is a schematic representation of a nebulizer illustrating a
further mode of operation according to the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
In FIGS. 1 and 2 an ultrasonic nebulizer is shown generally at 1.
The nebulizer 1 of FIGS. 1 and 2 has the same basic components but
different modes of operation, which modes will be described
separately for each of the FIGS. 1 and 2.
The ultrasonic nebulizer 1 of FIGS. 1 and 2 includes a ultrasonic
oscillator 2, here in the form of a piezoelectric transducer, which
is located in a water chamber 3 above which is a nebulization
chamber 4. A liquid 5 for nebulization is held within the
nebulization chamber 4 so that in use a space into which nebulized
liquid passes remains in the chamber 4 above an upper boundary 6 of
the liquid 5. Gas may be introduced into the nebulization chamber
4, flowing from an inlet 7 to an outlet 8 through the space above
the upper boundary 6, and removing from the chamber 4 liquid
droplets formed during nebulization. A thin membrane 9 separates
the water chamber 3 from the nebulization chamber 4 so that
ultrasonic energy from the oscillator 2 can pass readily
therethrough with the result that the oscillator 2 "sees"
essentially only a single body of liquid, terminating at the upper
boundary 6. An oscillator driver 10 is connected in an electrical
circuit with the oscillator 2 and is arranged to drive the
oscillator 2 to generate a controllable, variable amplitude
ultrasonic signal for emission into the water chamber 3. A sonar
detection stage 11 is also provided in electrical connection with
the oscillator driver 10 and with the oscillator 2. The detection
stage 11 includes conventional timer circuitry (not shown) which is
arranged to measure the transit time for an ultrasonic sonar pulse
to travel from the oscillator 2 to the upper liquid boundary 6 and
back again. The detection stage 11 is also adapted to emit a signal
representative of this measured transit time.
The driver 10 and the sonar detection stage 11 are readily
realizable by those skilled in the art using conventional
electrical engineering methodology and an understanding of the
principles of their function, as provided herein.
A controller unit 12, for example in the form of a suitably
programmed computer, is operably connected to both the driver 10
and the sonar detection stage 11 and provides control of the driver
10 and calculates the location of the upper liquid boundary 6
within the nebulization chamber 4 from the output signal of the
sonar detection stage 11.
To explain the nebulizer 1 of FIG. 1 and its mode of operation, the
arrows 13 show the path of the sonar pulse. In use the controller
unit 12 provides control instructions to the driver 10 for
generating a periodic variation in the amplitude of the ultrasonic
energy emitted by the oscillator 2. The variation is such that
nebulization periods, during which high amplitude ultrasound are
emitted which are sufficient to cause nebulization, alternate with
measurement periods, during which only ultrasound sonar pulses are
emitted having an amplitude, insufficient to affect i.e. disturb,
the location of the upper boundary 6 to a measurable extent.
During a measurement period a trigger signal is sent to the sonar
detection stage 11, corresponding to the oscillator 2 being driven,
to generate an ultrasonic sonar pulse. The trigger signal, which
may conveniently be provided either by the controller unit 12 or
the driver 10, initiates the start of timing by the timer
circuitry. The time measurement is stopped when the receipt of a
reflected component of the generated ultrasonic pulse is detected
at the oscillator 2. This detection is facilitated by the use of a
piezoelectric transducer as the oscillator 2. It is well known that
ultrasonic energy incident on such a piezoelectric transducer 2 can
cause detectable changes in the electrical properties of an
electrical circuit in which the transducer 2 is included. Thus in
the present embodiment the receipt of the reflected pulse is
detected using such known circuitry within the detection stage 11.
The pulse emission and detection optionally can be carried out a
number of times throughout the measurement period and an average
location determination made within the controller unit 12 based on
the averaged value of the measured transit times. The determined
location may be used within the controller unit 12 to provide a
control signal which inhibits the operation of the driver 10 when a
location corresponding to a minimum level is detected.
Optionally, the controller unit 12 may be programmed to compare the
currently determined location with a previously determined
location, having a known temporal relationship to the currently
determined location and preferably one made in a consecutive
measurement period, so that the amount of liquid nebulized during
an intervening nebulization period or periods may be calculated
within the controller unit 12 to provide dose information. This
dose information may then be used by the controller unit 12 in the
control of the driver 10 to regulate one or both of the amplitude
of the ultrasound generated for nebulization and the duration of
the nebulization period to obtain a desired dose from the nebulizer
1.
For explaining the nebulizer 1 of FIG. 2 and its mode of operation,
solid arrows 14 and dashed arrows 14' show paths of the sonar
pulses. In use the controller unit 12 controls the driver 10 to
provide the piezoelectric transducer 2 with a known, variable
amplitude driving force to generate a corresponding variable
amplitude ultrasonic output into the water chamber 3. The driver 10
is controlled to provide from the oscillator 2 at least one
nebulization period, during which high amplitude ultrasound is
emitted sufficient to cause nebulization, and at least one
measurement period, during which ultrasound is emitted at
amplitudes lower than are capable of causing nebulization.
During each measurement period the controller unit 12 controls the
driver 10 to generate at least two different amplitudes of
ultrasound to provide distinguishable and different locations of at
least part of the upper boundary 6, 6'. As illustrated in FIG. 2
one output amplitude is chosen so as not to affect (i.e. disturb)
the location of the upper boundary 6' to a measurable extent, for
example a zero amplitude output, and the other output amplitude is
chosen to provide a localized change in the upper boundary 6. The
sonar detection stage 11 and the driver 10 operate cooperatively to
provide two measurements of transit times; one for a sonar pulse
traveling along the path 14 which measures the location of the
boundary 6, and the other for a sonar pulse traveling along the
path 14' which measures the location of the boundary 6'. These
measurements are carried out in a manner analogous to that
described for the transit time measurements of FIG. 1.
The controller unit 12 is operably connected to the sonar detection
stage 11 to receive outputs from the detection stage 11
representative of the two measured transit times. A difference
calculation between the locations of the boundaries 6, 6' is made
within the controller unit 12. The controller unit 12 is further
adapted to calculate the rate of change of location of the boundary
with supplied driving force using the calculated difference and
from the knowledge of the amplitude of the driving force supplied
by the driver 10 to generate the two upper boundary locations 6,
6'. From this rate of change the controller unit 12 generates an
estimate of the driving force required to be provided to the
oscillator 2 in order to generate a desired degree of nebulization
within the nebulizer 1 and controls the driver 10 accordingly.
Although modifications and changes may be suggested by those
skilled in the art, it is the intention of the inventor to embody
within the patent warranted hereon all changes and modifications as
reasonably and properly come within the scope of his contribution
to the art.
* * * * *